An electromagnetic generator having a pendulum structure has conventionally been known as an intra-tire power generating unit to be mounted on an inner surface of a tire (see Patent Document 1, for instance).
The electromagnetic generator is of such design that a permanent magnet swings like a pendulum relative to a coil inside a tire when the tire is rolling. In particular, high voltage is generated at both ends of the coil at the ground contact start point (leading point) and the ground contact end point (trailing point) where the pendulum is accelerated precipitously by the fore-aft acceleration occurring in the circumferential direction of the tire interior.
With an electromagnetic generator of the foregoing arrangement, shortening the equivalent pendulum length has been a way employed to reduce the inertia of the pendulum portion to improve power generation capacity.